SQL Server 2008记录头第一个字节各部分含义
- Byte 0 is the TagA byte of the record metadata.
- Bit 4 means the record has a NULL bitmap and bit 5 means the record has variable length columns. If 0x40 (bit 6) was also set, that would indicate that the record has a versioning tag. If 0x80 (bit 7) was also set, that would indicate that byte 1 has a value in it.
- Bits 1-3 of byte 0 give the record type. The possible values are:
- 0 = primary record. A data record in a heap that hasn't been forwarded or a data record at the leaf level of a clustered index.
- 1 = forwarded record
- 2 = forwarding record
- 3 = index record
- 4 = blob fragment
- 5 = ghost index record
- 6 = ghost data record
- 7 = ghost version record. A special 15-byte record containing a single byte record header plus a 14-byte versioning tag that is used in some circumstances (like ghosting a versioned blob record)
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